I have a 04 sierra 2wd excab. My transmission won't shift into 3rd gear unless u Rev it up to around 3500 and ease off the gas and it will shift out. Any thoughts on what's wrong? Also my friend has 05 4wd wrecked tahoe will his transmission work in my truck? Or is there anyway that I can make it work?

 

Assuming both trucks have 4l60E's, yes they will interchange, but you'll have to swap the tail housings between the two transmissions

 

The Entire 4L60E Transmission would have to be disassembled to change the Output-Shafts from Two-Wheel Drive to Four-Wheel Drive or vice-versa.